once you set it lower then the width of your vinyl, you may sacrifice more efficiency on one axis to gain a lesser amount of efficiency on the other axis. Consider 6" long script with lots of letter centers to cut out. Now consider 12 copies of this running perpendicular to the width of the vinyl. If set at 10... Flexi could finish each single continous outer contour and all letter centers before moving an inch across & finishing the next, then the next. But if set at 5, you are telling it to go 13" across the length of the vinyl cutting out the letter centers from one copy to the next & back again before ever finishing the first word.
Maybe not the best example, & probably splitting hairs as far as actual time lost, or saved... but as a conceptual puzzle, I think that is my final answer